In plastic materials such as polyvinyl chloride, the use of fillers is known. The presence of the fillers is known as a means of imparting dimensional rigidity, coloring, weathering, and lower costs of final plastic materials. However, advantages of fillers are balanced against at least one disadvantage including (i) slower processing during manufacture of the plastic materials, and (ii) diminished impact strength.
In order to overcome a number of the difficulties highlighted above, attempts have been made to employ coupling agents or other additives to the filler to promote compatibility with plastic materials.
U.S. Pat. No. 3,778,287 discloses structures of poly 12-hydroxystearic acids (PHS) and polyricinoleic acids (PRA) and their use in aliphatic/aromatic ink/paint systems as dispersants for organic and inorganic pigments.
Application and use of processing additives containing repeat units from hydroxycarboxylic acids are suggested for particulate solids by U.S. Pat. No. 4,797,440 in general thermoplastics. PVC is mentioned (column 4) and exemplified in Example 37 of Table 9 of the patent (Column 11). The particular Example 37 includes a phthalocyanine blue (0.2 g/100 g PVC) and titanium dioxide (2 g/100 g PVC) and exemplifies the increased colour strength generated by use of these dispersants. Advantages (end of column 1 and start of column 2) attributed to the use of the processing additive were fewer specks and better surface finish. The polymers were primarily polyolefins. Interestingly, chlorinated PVC and urethanes are not specifically mentioned as operative thermoplastics.
Trying to get the PHS or PRA dispersant onto filler (filler treatment) is covered by GB 2 056 461 where an emulsion is made of the dispersant and then applied to the pigment/filler surface. Again, examples of using the treated pigment in a PVC formulation are given (Example 45-47 bottom of page 7). Again, colour strength and reduction of speck levels are the major improvements from using such dispersants.
Formulating polymers from vinyl chloride for melt processing presents numerous issues and a need to balance processing properties and final properties. Polymers of higher molecular weight (high inherent viscosity (IV)) typically have better properties such as strength and impact resistance, but melt process at slower rates than lower molecular weight polymers of the same composition. The addition of Impact modifiers to polymers from vinyl chloride provide important impact resistance to molded articles but also slows melt processing rates. Particulate fillers can be added but also decrease melt processing rates. Thermal degradation of vinyl chloride based polymers accelerates as degradation products like HCl are produced from past thermal exposure of the polymer. Therefore, it is desirable to minimize the melt temperature and thermal exposure time of polymers from vinyl chloride. The thermal exposure both imparts a yellow color to the polymer and lowers the molecular weight, of the polymer. Contradictory to the desire for short thermal history is the necessity to fully melt and fuse the polymers from vinyl chloride during melt processing to achieve optimal impact resistance and strength in the final article.
PHS/CAP and PRA/CAP polymers (CAP stands for caprolactone) have been disclosed as intermediates to PEI dispersants in U.S. Pat. Nos. 5,700,395 and 6,787,900. They have not generally been claimed as dispersants themselves except in US Publication 20060189502A1 for Dispersions to Make Electronic Devices, such as electrical capacitors containing electrically conductive metal layers and electrically insulative layers laid downed and then fired to form a ceramic composite.
It would be desirable to have a class of dispersants in filled poly vinyl chloride compositions, to dispersions containing such dispersants together with a particulate solid in PVC, and compositions comprising a particulate solid, PVC and a dispersant which require a shorter melt processing time. It would also be desirable to have a dispersant to use in forming finished PVC articles, which may optionally have filler present, that promotes fusion of the PVC particles and thereby enhances throughput through the PVC processing equipment.